Tillering new guinea teak flatbow

[Benjin Khan]

Hi all,

I've just started tillering my flatbow made from new guinea teak. Just got it to brace height and left it strung overnight last night.
It's drawing 20lb at 6 inches of brace height and I'm aiming for 45-50lb @ 32 inches. I'm not sure how much it should start at so I'm open to comments here - I've read you can work on about 1.5lb gain per inch?

The bow is 78 inches nock to nock as I have a 32 inch draw length. Not sure if this is too long - the handle section is about 400mm before any bend starts.

I have used photoshop to check the symmetry of the limbs and they are very similar. To my eye though it looks like the right hand (upper)limb is bending slightly more than the other.

I'd welcome comments from anyone with an experienced eye - this is only the 3rd bow I've made and it's been along time since the last one so I'm doing lot's of reading trying to take it slow. It's hard not to rush it because i can't wait to shoot it!!


Cheers, Ben.

[greybeard]

Leaving the bow braced overnight may lead to increased string follow.

Daryl.

[Benjin Khan]

Leaving the bow braced overnight may lead to increased string follow.

Daryl.

Really? bugger - the only reason I did it is because I read it prevents string follow once it is fully tillered

[twisted limb]

Thats comming along nicely Ben,the outer limbs are still very stiff.Interesting choice of wood teak is very dense isn't it?
You are just encouraging string follow leaving it strung overnight I would think.
John.

[Steven J]

Really? bugger - the only reason I did it is because I read it prevents string follow once it is fully tillered

There are a lot of ideas out there...

Every try finding North using a shadow stick. It is in every survival book under the sun and explained again on probably hundreds of websites as a true and reliable method. Truth is it is really only a best guess +/- 30 degrees.

It is hard when you are learning to sift the wheat from the chaff. For those of us that are learning we have Greybeard.

Steve

[Keith Lee]

Looking good Ben i've made 5 and they've all broke before i even got to that stage try again soon with some Red Ash. Cheers yowie.

[KellyG]

I think it looks really good so far. The only advise I can give is to keep it off the long string now and just use your short string to tiller it in. Good luck,
Kelly

[Benjin Khan]

Thanks Kelly, that's what i'm planning to do. I've read it will give a more realistic bend particularly on the tips.

Ben

[Dennis La Varenne]

Ben,

That tillering job looks pretty spot-on to me, beautiful in fact, but notice that Daryl said

may lead to increased string follow

.
It is not inevitable, but neither would I leave it so long either.

My suggestion only on this (not from personal experience) would be that if it did achieve the maximum amount of string follow from being so left, there is a fair probability that the string follow would be pretty sizeable from being under constant bending load for such a long time rather than the more impulsed loads of normal tillering.

Having said that, my technique which mortifies some, but which has give me pretty good low string follow results has been - once the bow tillers well to a good brace height - I then increase the bend on the tiller one step at a time right out to full draw, watching like a hawk and constantly feeling the surfaces for problems. I don't take it down from the tiller at all during this last combined tiller-break in stage.

If it keeps true and the wood stays sound out to full draw length, I then leave it on the tiller at full draw for perhaps the time of a cup of tea and then come back, check it and then take it down. I then shoot it.

Originally, I thought I would have some terrible string follow problems, but it didn't happen which was a real surprise to me and totally unexpected. I did it to see what would happen really and nothing (bad) did. This is not a technique I would recommend for a newbie, necessarily. There are a lot more more conservative techniques than mine, but I want to get the process over and done with and not prolong the agony.

It is not an impatience thing. If it is going to break, then I want it to break as soon as possible and have done with it. Then I know to begin on another. I have never had a bow break from this technique after I started it. Any breakages have always followed and been traceable to a fault in the wood.

Anyway, the upshot of what I am on about is that prolonged time on a tiller is not a guarantee of string follow so long as the intended draw length-draw weight nexis is not exceeded by much. Inevitably, materials fatigue will induce some string-follow. I think that is something we can accept. Bear in mind that string follow does not necessarily mean that the limb tips are behind the belly of the bow. For instance, string-follow is also when a bow with some limb reflex loses some of that from the original amount. It isn't all bad.

I did my Photoshop thing on your tiller pic and it shows the very slightest amount of positive tiller which you can see from the areas A and B.

With your grip type which shows a preference for a high wrist grip, I would say that you could almost certainly weaken your lower limb slightly and bring the whole bow to almost zero tiller, but only if you are a true high wrist shooter. If you grip the bow, stay with what you have to keep the limb timing at optimum.

One further thing, your bow is a bit out of square to the line of your tiller which makes it tip low to the right by the order of 12 degrees as indicated by the blue horizontal line. This can cause the bow to change its tiller once taken down if you work on it whilst it lay on the tiller this way. The stem of a tiller will block the transfer of the bending load right across the whole bow and keep it to the one limb. With the right hand limb down, you can easily 'under-tiller' that limb . . . thinking that because its tip is bending as far down on the horizontal as the left limb, everything is even.

Not many people realise this. It is one particular justification for removing the bow from the tiller from time to time even though above, I have said differently. During the early phases of tillering, always take it down to have a look at what it happening. It is almost always different to what is happening on the tiller. And always look at your bow from the other side as well. It is marvellous how different it can look from the other side.

[Benjin Khan]

Well I did some more tillering this afternoon - full of optimism and armed with lot's of helpful advice, but it wasn't to be.

I had it down to 27 inches, all looking good........'CRACK'.......

It didn't explode straight away and I got one dodgy photo of the crack before it let go (I tried to move the tillering tree into better light and it exploded)
I could see a small change in the grain in that spot - I guess it only takes one small flaw.

Time to start a new one! I might see how my mate's turns out before I try this timber again - he is about to start tillering.

[Dennis La Varenne]

Ben,

That looks like a classic tension break from the way in which the wood fibres have let go and one of your pictures. That wood is probably OK under compression on the belly, but clearly needs a good backing layer before any serious bending takes place. It may well be a candidate for one of the very thin Bamboo backing layers from that vertical flooring material or perhaps a native wood such as Spotted gum which is very good in tension.

Don't lose heart in the wood specie altogether. It is such a shame when that happens. All of us feel for you.

Just ask Jeff how that feels. He knows exactly.

[yeoman]

I have a couple of words of encouragement for you.

Firstly, in your pic of the bow on the long tiller string, you are well justified in tillering it such that the outer limbs look a bit too stiff. This is a Good Thing, because the leverages exerted on the bow limb with a long tiller string are different to those exerted by the shorter, Proper String.

In the broken bow pic the limb broke into three pieces. Believe it or not this is acutally a good sign. Wood breaks when the stresses placed upon it exceed the mechanical properties it is capable of withstanding. The fact that the bow limb broke in more than one place means that although the limb was stressed more than it could withstand, at the very least you were tillering it evenly throughout.

Steve Gardner, who was (I think still is) the world record holder for primitive bow flightshooting breaks hundreds of bows a year looking for their limits. His tillering is so good that when his bows break they regularly break into anywhere from 4-12 pieces. So you're almost breaking the bow like a world record holder!

Your tiller shape with the short string on looks quite good too. Quite round though. Was this bow a pyramid bow, or close to it? It looks as if it is based on the broken bow limb pic. With a bow of that length, I might recommend a limb plan which has the limbs parallel for maybe a third to one half the limb's length, then at 3/4 of the way out to the tip make it 3/4 of the original width. The curve can be drawn by marking the major points, then bending a 1 metre steel ruler to touch all the points. Unless you are quite dextrous, you may need someone else to draw this line.

bow plan.jpg (62.54 KiB) Viewed 4036 times

This of course means it will need to taper in thickness too, but that will sort itself out in the tillering process. But, if you cut it out such that the thickness starts at maybe 5/8" at the fades, straight line taper to 1/2" at 3/4 of the way out along the limb, then straight line down to 3/8" at the nock, will likely give you a good start.

Or not. People can do as they wish so you can feel free to ignore me.

Dave

[Dennis La Varenne]

Ben,

Have a very good read of Dave's post above.

[kimall]

Dennis have you had good results with the vert flooring as backing as I find it good on the belly but have never had any success with it as a backing.Always cracking across the limb even if the main timber does not break.
Cheers KIM

[Dennis La Varenne]

Kim,

Not my direct experience. Only referring on what other posters on Ozbow have recommended with the vertical bamboo. I should have made that clear.

The stuff seems to be held in pretty high regard as backing and as core lams as well. I think Daryl may have done some work with it.

Although not related to Ben's problems above, I am interested in your experience which is the first I have heard of. Can you describe what actually happened and how exactly did the break occur? I have only ever read about it failing in compression on Ozbow that I can recall. I must do a search of posts and check up.

Bamboo is renowned for its resistance to tension, whether laminated or not. Your experience could well be cautionary for the rest of us. I have always thought it far too strong for most belly woods unless used as Yeoman uses it as a fairly narrow backing strip and fairly thin, but that is not vertical lam as I recall.

[kimall]

I made some grey ironbark bows a while ago and they came up a bit light so backed them with a lam of the vert bamboo because I had such good results on the belly before but on both the lam cracked straight across the back of the limb but only the backing ,the bow was fine and I was able to take the boo off and put other backing on.I have only used the floor board boo though not REAL boo.
Cheers KIM

[greybeard]

Kim,

Vertical bamboo flooring appears to have very little if any power fibres.

I love it as core material under glass because of its consistency when used as a spacing material and its lower mass.

The fibre structure of processed bamboo flooring is very hydroscopic so a good dose of superglue or Techniglue on the surface may help bond the fibres if you wish to use it as backing/belly material.

I only ever use pole bamboo as back and belly material.

Daryl.

[kimall]

Yep my thoughts exactly Daryl.It was early on in my bow making that is why I am looking at getting the prop boo now.
It is VERY hydro what you call it I found it will grow mould almost overnight if you allow.
Cheers KIM

[Benjin Khan]

Thanks for your comments Dave and Dennis, I'm trying to absorb as much as I can. That's very encouraging to know that the experts are breaking bows as well!

I sort of knew that bow breaking was part of bow making, but it's the first one I have broken myself. I had a couple explode next to me when I was making my first one back in high school (that was the best wood shop class we ever had!)

I'm very interested to try a backing of bamboo. Do you need a hotbox to do laminated bows or can you get away without it?
I like the look of the flooring products because they are already straight and flat. Are there ones that are better than others to use?
I found these 2 types of lamination - by instinct I'd go for the one with solid bamboo from top to bottom of the board (pic 2) seems like there wouldn't be as much stress on the glue joins.

Dennis, when you said very thin, would 3mm about right?

[Benjin Khan]

Your tiller shape with the short string on looks quite good too. Quite round though. Was this bow a pyramid bow, or close to it? It looks as if it is based on the broken bow limb pic.

My limb shape was a straight taper from the fade to tip, with the thickness the same all the way to the tip. I just based this on the previous one i had made as it's still shooting ten years on.

One thing I should mention is it was pulling about 35lb when it broke.

Do you think a pyramid design would have prevented or reduced the likelihood of the break? I didn't think it was a result of bad tiller shape.

Ben

[yeoman]

My limb shape was a straight taper from the fade to tip, with the thickness the same all the way to the tip. I just based this on the previous one i had made as it's still shooting ten years on.

It is as I suspected then. There is nothing wrong with a pyramid bow design. They are durable, easy to tiller and ensure even stress along the limb. They are not more or less likely to cause a bow to break. However, a circular tiller, pyramid bow shape is best used on a shorter bow. A longer bow, when compared to the draw length, benefits more from having eliptical tiller, which bends more at the tips and less at the handle. This reduces the amount of mass the bow has to move forward when you release the string, which means more energy is available to propel the arrow.

I've heard from many people that vertical bamboo is a bad backing, due to a frequent tendency to splinter and break. My understanding is that this is not due to a lack of power fibers (evidenced by the fact it makes a good belly lam), but rather because in the manufacturing process, the factory does not care if the surface of the board runs parallel to the surface of the board. They think people will only be walking on thier product, so a bit of grain violation does not matter. To them, anyway.

Dave

[Dennis La Varenne]

Ben,

I am more surprised than anyone that bamboo flooring is not well thought of now as a backing layer. It went through phase as flavour of the month for just about anything a couple of years back. However, what Dave is saying about the manufacturing process makes sense to me. It is designed to be walked on rather than bent I suppose.

If you can get strip bamboo with the nodes still on and not ground off flat, I think Dave above grinds the inside below the rind to only a couple of mm thick for his bows and leaves it a bit narrower than the limb width for tension-compression balance. He can explain his technique. Do a search on 'Yeoman' to find his articles.

However, he also once wrote up a very clever bending test to test the actual strength of the bit of wood you are using at the time in his article on using maths in making bows. Modestly I suspect, he is not blowing his trumpet.

Also,

In the broken bow pic the limb broke into three pieces. Believe it or not this is acutally a good sign. Wood breaks when the stresses placed upon it exceed the mechanical properties it is capable of withstanding. The fact that the bow limb broke in more than one place means that although the limb was stressed more than it could withstand, at the very least you were tillering it evenly throughout.

Steve Gardner, who was (I think still is) the world record holder for primitive bow flightshooting breaks hundreds of bows a year looking for their limits. His tillering is so good that when his bows break they regularly break into anywhere from 4-12 pieces. So you're almost breaking the bow like a world record holder!

this is about the most constructive thing I have ever seen written on the sad experience of breaking a bow in the making.